Calcium Channel Blockers
Calcium channel blockers (CCBs) are a chemically diverse class of compounds having important therapeutic value in the control of a variety of diseases including several cardiovascular disorders, such as hypertension, angina, and cardiac arrhythmias and include a heterogeneous group of drugs that prevent or slow the entry of calcium into cells by regulating cellular calcium channels. Calcium influx through these channels initiates a process of electromechanical coupling that ultimately leads to muscle contraction. The ability to regulate the entry of calcium into cardiac and vascular smooth muscle cells is a powerful therapeutic approach to the treatment of angina and hypertension, respectively. Likewise, blocking calcium influx into cardiac tissues and conduction systems provides a useful approach to control certain types of arrhythmia. Most of the currently available calcium channel blockers belong to one of three major chemical groups of drugs: the dihydropyridines, such as nifedipine, the phenylalkylamines, such as verapamil, and the benzothiazepines, such as diltiazem.
Serum Esterases
Serum esterases play an important role in the hydrolytic biotransformation of a vast number of structurally diverse drugs. These enzymes are major determinants of the pharmacokinetic behavior of most therapeutic agents containing ester bonds. Serum esterases are classified into three groups, A- B- and C-esterases, based on their interaction with organophosphates (De Vriese et al., Endocrinology (2004) 145, No. 11, 4997-5005). A-esterases, including arylesterase/paraoxonase, rapidly hydrolyze organophosphates. B-esterases, including acetylcholinesterase, butyrylcholinesterase, and nonspecific carboxylesterase, are inhibited by organophosphates. C-esterases, such as acetylesterase, do not interact with organophosphates.
Angina
Angina is a symptom of insufficient blood oxygen supply to an area of the heart due to an imbalance of the oxygen supply-demand ratio. Angina is usually precipitated following exertion, or emotional stress in susceptible patients due to an inability of the coronary vasculature to provide sufficient cardiac oxygen perfusion. A narrowing of the coronary arteries is often an underlying cause as a result of arteriosclerosis or vasospastic narrowing of blood vessels. Angina usually lasts less than 15 minutes and is typically treated by sublingual administration of nitroglycerin to relieve symptoms. Nitroglycerin and other nitrates induce vasodilation through release of nitric oxide (NO) thereby causing a lowering of blood pressure.
Angina can he classified as stable angina whose principal underlying cause is arteriosclerosis, vasospastic angina (also called variant angina or Prinzmetal angina) whose underlying cause is due to transient vasospasm of the coronary arteries, or unstable angina caused by platelet clotting at sites of ruptured arteriosclerotic plaques. Stable angina usually occurs as a result of exertion or stress whereas vasospastic angina can also be felt during periods of rest or in the early morning hours. Unstable angina is felt even during periods of rest and can signal imminent myocardial infarction. Sustained reduced blood flow (ischemia) to the heart can cause permanent damage to the heart due to the death of cardiac muscle. When coronary arteries are severely narrowed by more than 50-70%, the blood vessels can no longer supply the oxygen demands of the heart and angina is felt symptomatically as chest pain.
Cardiac Arrhythmia and Atrial Fibrillation
Arrhythmia, or abnormal heart rhythms, is caused by abnormal excitation and conduction to the heart. The mechanism of the onset of arrhythmia is categorized into three groups: (1) abnormal excitation, (2) abnormal conduction of excitation, and (3) a combination of abnormal excitation and abnormal conduction of excitation.
Atrial fibrillation is arrhythmia arising from abnormalities in the intrinsic pacemaker conductive potential of the heart. In atrial fibrillation, the electrical discharges are rapid and irregular, resulting in an irregular rhythm of heart contraction. In a normal heart, electrical discharges are generated in the sino-atrial node. In atrial fibrillation, electrical discharges are not generated exclusively in the sino-atrial node and come from other parts of the atria. These rapid and irregular discharges result in rapid and ineffectual atrial contractions that reduce the ability of the atria to supply blood to the ventricles.
A recurrent arrhythmia with an abrupt onset and termination is designated as paroxysmal. Paroxysmal supraventricular tachycardia (PSVT) presents as episodes of regular and paroxysmal palpitations with sudden onset and termination (Blomstrom-Lundqvist et al., 2003, J Am Coll Cardiol, 42:1493-531).
Atrial flutter is characterized by acute symptoms of palpitations, dyspnea, fatigue, or chest pain. In most instances, patients with atrial flutter have a two-to-one atrio-ventricular node (AV) conduction pattern. For example, the flutter rate of the atria can be 300 per minute with a ventricular rate of 150 beats per minute (Blomstrom-Lundqvist et al., 2003, J Am Coll Cardiol, 42:1493-531).
Blood Flow and Pressure Regulation
Hypertension is defined as high blood pressure, usually above 140 (systolic)/90 (diastolic). Hypertensive conditions can occur in relation to the conduction of surgical procedures. For example, blood pressure control is critical before, during, and after surgery. Hypertensive crisis arising from high blood pressure is subdivided into two categories: urgent and emergency. The symptoms of an emergency hypertensive crisis are more severe and may include brain swelling, stroke, pulmonary edema, heart attack or other symptoms. Both urgent and emergency categories hypertensive crisis involve a severe increase in blood pressure and require immediate treatment to prevent potential complications (i.e., stroke or damage to organs and tissues).
Raynaud's phenomenon is a disorder associated with restricted blood flow to body extremities such as the fingers, toes, ears and nose, and reflects an aberration of the normal response to cold involving peripheral vasoconstriction and restriction of blood flow to the extremities in order to protect the core body temperature. Attacks may be brought on by exposure to cold or emotional stress. Up to 5 to 10% of the population of the United States is affected, to some degree, by Raynaud's phenomenon.
Intermittent claudication is a condition that involves discomfort in the legs and occasionally the arms. It is due to a narrowing of the arteries and a resulting decrease in blood flow, particularly to muscles during physical exertion. The condition most commonly occurs in the calf muscle but may also affect the foot, hip or buttocks.
No-reflow phenomenon is a condition following reperfusion in which excessive or abnormal vasoconstriction occurs. The no-reflow phenomenon that occurs in about 2-5% of patients undergoing percutaneous transluminal coronary angioplasty (PTCA) is believed to be due to aggregation of platelets and neutrophils, which causes a blockage of blood flow within the vessels and vasoconstriction from substances released from the platelets. The condition is characterized by abnormal tissue perfusion. Persistent no-reflow is associated with higher clinical complication rates (Eeckhout, E. and Kern, M. J., European Heart Journal (2001) 22, 729-739).
Given the prevalence of cardiovascular disorders in patients, there is a need for new and improved compound and methods for treating cardiovascular disorders including ischemic heart conditions and cardiac arrhythmias.